The present invention relates to a mounting system for a flame pipe or liner, in particular a system for mounting a flame pipe or liner inside a combustion chamber of a gas turbine with low polluting emissions.
The present invention relates to a mounting system for a flame pipe or liner, in particular a system for mounting or fixing a flame pipe or liner inside a combustion chamber of a gas turbine with low polluting emissions. As is known, gas turbines are machines consisting of a compressor and a turbine with one or more phases, wherein the compressor and turbine are connected to each other by a rotating shaft and wherein, between the compressor and the turbine, there is a combustion chamber. Air from the outside environment is fed to the compressor to bring it under pressure. The pressurized air passes through a duct, terminating with a convergent portion, inside which a series of injectors feeds fuel which is mixed with the air to form an air-fuel mixture to be burnt.
The fuel necessary for producing combustion, which causes an increase in the temperature and enthalpy of the gas, is therefore introduced into the combustion chamber by means of one or more injectors fed by a pressurized network.
Finally, the high temperature and high pressure gas reaches the various phases of the turbine, through specific ducts, which transforms the gas enthalpy into mechanical energy available for a user.
It is known that in the engineering of combustion chambers for gas turbines, the main considerations are dedicated to flame stability and control of the excess air to bring the combustion under ideal conditions and minimize the production of polluting substances. More specifically, the known art envisages the use of a flame pipe or liner inside the combustion chamber, which has two main functions. In the first place, the flame is contained inside the pipe to prevent its contact with the outer parts of the combustion chamber, in order to avoid overheating. Secondly, the pipe slows down and diffuses the flow of combustion products preventing the flame from being extinguished.
The flame pipe according to the known art is made of a metallic material, thus making it easy to fix inside the chamber and making it compatible, with respect to the tensional states generated by the thermal expansion, with the other structural components of the combustion chamber also made of metallic material. As a result of their limited mechanical characteristics under heat, however, the traditional liners or flame pipes have limits in reaching high combustion temperatures and require a high quantity of cooling air passing through them. The high quantity of cooling air required by metallic liners negatively influences the separation of the exhaust emissions.
In order to overcome these drawbacks, liners or flame pipes made of a composite material with a ceramic matrix, such as silicon carbide, have been proposed. These liners allow the following results to be obtained: an increase in the combustion temperature and consequently in the yield of gas turbines, a decrease in the cooling air in the combustion area thus facilitating the production of low emissions and, finally, an increase in the useful life of the components subjected to high temperatures. These liners or flame pipes are installed inside the combustion chamber, through sleeves made of a metallic material, situated at the ends of the liner and in turn, fixed, by means of welding or other known means, to metallic portions of the combustion chamber.
The different thermal expansion coefficient between the ceramic material and metal can, however, cause dangerous tensional states in the thermal expansion phase, which can jeopardize the resistance of the ceramic material and its duration with time. Furthermore, the fixing or mounting means so far envisaged, do not protect the ceramic material of the liner from the damaging scratching thereon of the metallic connecting portions of the combustion chamber.